You can do this in AIR. Create a simple AIR app that is an invoke target for the text to have it save it to a PDF. BBW is suppose to support invoke targets at some point, so if the user does not have it installed, BBW will prompt them. Until BBW has it, you can query the targets and if it is not installed, re-direct the user to BBW to download the app.
May as well make the invocation public so other apps might be able to use it.
I would personally try to use an webservice, as mentioned by javayoung.
But if you really want to do it on the device (because of large files, no internet access..) then I would also use the solution from jtegen. Maybe there are some apps out there which already provide this feature, so maybe have a look for them first.
If not, I've read a post about it, where it was explained how you can do this, so just do an internet search for more info.
A like is always appreciated, but a nomination for BB Elite even more :-) You can also contact me on Twitter: @ndsmyter